Snowmobile suspension system

ABSTRACT

A snowmobile includes a pair of skis connected to the snowmobile frame by a forward suspension including a pair of telescopic struts which are biased to normally extended positions and are connected to a stabilizer member including a transverse torsion bar. A drive track of the snowmobile is suspended from the frame by a rear suspension, including a link pivotally connected between the frame, and a pair of slide rails and biased downwardly by a pair of torsion springs having respective ends engaged with a pivotally mounted spring end retainer which is connected to the torsion bar of the forward suspension by a pair of motion transfer links which act to &#34;soften&#34; the rear suspension in response to upward telescopic movement of one or the other or both of the telescopic struts.

BACKGROUND OF THE INVENTION

The present invention relates to suspension systems for snowmobile skisand drive tracks and more specifically relates to such suspensionsystems which include a stabilizer bar and telescopic strut assembliesfor the skis.

Heretofore, suspension systems for snowmobiles have included frontsuspensions for the skis and separate rear suspensions for the tracks.An example of a front suspension, including a pair of telescopic struts,is disclosed in copending U.S. patent application, Ser. No. 140,730,filed by S. G. Hayes on April 16, 1980, which issued on Aug. 3, 1982 asU.S. Pat. No. 4,342,372. An example of a rear suspension is disclosed inU.S. Pat. No. 3,913,692, granted to Lohr et al on Oct. 21, 1975. Whileit is known to include stabilizer bars as portions of front suspensionsfor snowmobiles, such stabilizer bars have been used only in conjunctionwith front suspensions, including leaf springs attached lengthwise onthe tops of the skis as disclosed, for example, in U.S. Pat. No.3,835,947, granted to Alexander on Sept. 17, 1974.

SUMMARY OF THE INVENTION

According to the present invention, there is provided an improvedsuspension system for a snowmobile.

An object of the invention is to provide a suspension system comprisinga front suspension, including a pair of telescopic struts connected toopposite ends of a stabilizer member.

A more specific object of the invention is to provide a frontsuspension, as set forth above, wherein the connection between thestruts and the stabilizer member transfers telescopic movement of thestrut to the stabilizer, but not steering movement.

Yet another object is to provide a suspension system where front andrear suspensions are interconnected such that the stiffness of the rearsuspension is decreased in response to one or the other of thetelescopic struts being compressed in response to load to thereby effecta more comfortable ride.

Another specific object is to provide interconnected front and rearsuspension wherein the stabilizer bar of the front suspension is linkedto a member for adjusting the torsional load in a pair of springsbiasing a slide rail assembly against the upper suface of the lower rowof a drive belt.

These and other objects will become apparent upon reading the ensuingdescription, together with the appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a left front perspective view of a snowmobile embodying asuspension system constructed in accordance with the principles of thepresent invention.

FIGS. 2A and 2B combine to form a left front perspective view of thefront and pertinent portion of the rear suspension and illustrate theinterconnection therebetween.

FIG. 3 is a left side elevational view of the left-hand telescopicstrut.

FIG. 4 is a sectional view taken along line 4--4 of FIG. 3.

FIG. 5 is a sectional view showing a portion of the linkage fortransferring certain front suspension movement of the rear suspension.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to FIG. 1, there is shown a snowmobile 10, including amain longitudinal frame 12, having right- and left-hand steerable skis14 and 15, respectively, suspended from the forward end thereof by afront suspension and defining a longitudinal tunnel 16 (FIG. 2B) havinga drive track 17 (FIG. 2B) disposed therein and suspended therefrom by arear suspension. The front and rear suspensions will presently bedescribed in more detail, together with right- and left-hand motiontransfer rods 18 and 20 which act to "soften" the rear suspension inresponse to the front suspension being loaded in a manner describedbelow.

Referring now to FIGS. 2 through 5, it can be seen that the skis 14 and15 are respectively suspended from the frame 12 by right- and left-handtelescopic struts 22 and 24. The strut 22 includes an upright outer tube26 fixed to the right-hand end of a transverse support member 28 formingpart of the frame while the strut 24 includes an upright outer tube 30fixed to the left-hand end of the member 28. Reciprocably and swivellymounted in the outer tubes 26 and 30 are inner tubes 32 and 34,respectively, which have their lower ends respectively pivotallyconnected to the skis 14 and 15 by bolts 36 and 38.

Respectively swivelly mounted on the lower ends of the fixed outer tubes26 and 30 are steering arms 40 and 42 having ears interconnected by atie rod 44. A steering input rod 46 is also connected to the ear 42 andreceives its input, as is conventional, from a steering post controlledby a set of handle bars 47 (FIG. 1). Connected between the steering arms40 and 42 and the skis 14 and 15, respectively, are hinges 48 and 49which serve to transfer steering motion to the skis while permitting thelatter to reciprocate with the inner tubes 32 and 34.

Located within each of the struts 22 and 24 and acting to yieldablymaintain them in normally extended conditions are identical spring andshock absorber assemblies which form part of a first biasing mechanismand of which only the right-hand one is illustrated and described indetail, for the sake of brevity. Thus, located within the right-handstrut 24 is an extensible and retractable shock absorber 50, including acylinder 52, having an end received on the bolt 36 and including a rod54 having an end fixed to the upper end of the fixed outer tube 26 by abolt 56. The cylinder 52 has a stepped exterior forming an upwardlyfacing shoulder 58 against which an annular spring retainer 60 isseated. A coil compression spring 62 is compressed between the retainer60 and an adjustment cam 64 engaged with the bolt 56.

Forming part of and acting to stabilize the front suspension, as whenthe snowmobile is travelling over moguls or being steered, is astabilizer assembly including stabilizer member 66. The stabilizermember 66 is formed, in part, by a transverse torsion bar 68, rotatablysupported on the frame 12 between and forwardly of the struts 22 and 24.The stabilizer member 66 further includes right- and left-hand straps 70and 72 having forward ends respectively fixed, as at 74 and 76, to theright- and left-hand ends of the torsion bar 68. Reciprocably mounted onthe outer tubes 26 and 30 are sleeves or collars 78 and 80,respectively, which are provided with inwardly projecting, offsetportions 82 and 84 forming pockets for providing clearance between thetubes 26 and 30 and the heads of bolts 86 and 88 that project radiallythrough the sleeves relative to respective longitudinal axes of thestruts 22 and 24. Right- and left-hand motion transfer links 90 and 92have respective ball joints at their upper ends connected to rear ortrailing ends of the straps 70 and 72 and respective ball joints attheir lower ends received on the bolts 86 and 88. Arranged equiangularlyin the sleeve 78 are three radially inwardly projecting pins 94 whichare respectively received in three longitudinally extending slots 96located in the outer tube 26. Overlapping and respectively extendingcrosswise to the slots 96 are three slots 103 located in the upper endof the inner tube 32. The inner ends of the three pins 94 arerespectively received in the three slots of the inner tube 32. Similarlyarranged equiangularly in the sleeve 80 are three radially inwardlyprojecting pins 100 respectively received in three long slots 102arranged longitudinally in the outer tube 30. The inner tube 34 isprovided with three slots (not shown) which extend crosswise to andoverlap the three slots 102 and the pins 100 project thereinto.

Thus, it will be appreciated that the sleeves 78 and 80 will reciprocatewith the inner tubes 32 and 34 due to the engagement of the latter withthe pins 94 and 100, but that the sleeves will not move when the innertubes 32 and 34 swivel due to the presence of the slots located in theupper ends of the tubes 32 and 34. Accordingly, when one or the other ofthe skis 14 and 16 is loaded so as to cause the respective strut toretract, the motion of the retracting strut will be transferred to thetorsion bar 68 by means of the associated one of the sleeves 78 and 80,the links 90 and 92 and the straps 70 and 72 and will act to tend tocause a similar retraction of the unloaded ski to thereby stabilize thesnowmobile 10.

This collapsing motion of one or the other of the struts 22 and 24 isalso transferred to the rear suspension of the snowmobile. Specifically,as can best be seen in FIGS. 2B and 5, the rear suspension includesright- and left-hand slide rails 104 and 106 which normally bear againstthe upper surface of the lower run of an endless belt forming the drivetrack 17. Respectively fixed to the rails 104 and 106 are a first pairof brackets 108 and 110 in which are received the opposite ends of atransverse pivot rod 112. Pivotally received on the rod 112 is a tubularmember 114 forming part of a U-shaped link 116 having its opposite legsprovided with forward tubular ends 118 and 120, respectively, pivotallymounted on a second transverse pivot rod 122 having its opposite endssecured to opposite right- and left-hand walls 124 and 126 of the tunnel16 formed by the frame 12. A second biasing mechanism acts to yieldablyresist movement of the slide rails 104 and 106, and hence the drive belt17 towards the frame 12. Specifically, received on the pivot rod 122inwardly of the link 116 is a tube 128 having a T-shaped spring-endretainer 130 fixed thereto. A right-hand torsion spring 132 has a seriesof coils received on the tube 128 and has one end formed into a hook 134engaged with the retainer 130 and a straight second end 135 slidablyengaged with a spool-like guide 136 mounted on the right-hand rail 104by a bracket 138. Similarly, a left-hand torsion spring 140 has a seriesof coils received on the tube 128 and has one end formed into a hook 142engaged with the retainer 130 and a straight second end 144 engaged witha spool-like guide 146 mounted on the left-hand rail 106 by a bracket148. The windings of the springs 132 and 140 are such that they tend toexert a force biasing the rails downwardly away from the frame 12against the lower run of the drive track 17.

Right- and left-hand levers 150 and 152, respectively, are pivotallyreceived on bushings 154 and 156 secured to the right- and left-handends of the pivot rod 122 by cap screws 158 (only the left one isvisible). The lower ends of the levers 150 and 152 respectively includeinwardly projecting legs 160 and 162 which terminate in upturned endsthat are fixed, as by weldments, to the tube 128.

Fixed to the torsion bar 68 of the front suspension, at a locationintermediate of its opposite ends, is an upstanding lever arm 164. Theright-hand motion transfer link 18 has its forward end pivotallyconnected, as at 168, to the upper end of the lever arm 164 and has itsrearward end pivotally connected, as at 170, to the upper end of theright-hand lever 150. Similarly, the left-hand motion transfer link 20has its forward end pivotally connected, as at 174, to the upper end ofthe lever arm 164 and has its rearward end pivotally connected, as at176, to the upper end of the left-hand lever 152.

Thus, it will be appreciated that upward movement of one or the other ofthe skis 14 and 16 will affect forward movement of the lever arm 164and, consequently, forward movement of the levers 150 and 152, whichresults in the spring-end retainer 130 moving forwardly to permit thesprings 132 and 140 to unwind so as to affect a "softening" of the rearsuspension in anticipation of whatever moguls or obstacles whichinitially caused the upward ski movement.

The operation of the snowmobile suspension is thought to be clearlyevident from the foregoing description and, for the sake of brevity, nofurther description of the operation is given.

We claim:
 1. In a snowmobile, including a frame, a front suspensionsuspending a pair of skis from the front of the frame for moving up anddown relative to the frame and a rear suspension suspending a drivetrack beneath a rear portion of the frame for moving up and downrelative to the frame, the front and rear suspensions respectivelyincluding a front pair of members which move up and down in concert withthe skis and a rear member which moves up and down in concert with thedrive track, and first and second biasing mechanisms, respectivelyacting between the frame and the front pair of members and the rearmember to bias the front and rear members downwardly relative to theframe, the improvement wherein the second biasing mechanism includes anelement mounted for movement in a first direction for decreasing theresistance of the second biasing mechanism to upward track movement asthe displacement of the element in the first direction increases, and amotion transfer linkage means, connected between the front pair ofmembers and the element, for transferring upward movement of the frontpair of members to the element for moving the latter in the firstdirection to thereby decrease the resistance of the second biasingmechanism of the rear suspension to upward track movement.
 2. In asnowmobile, including a longitudinally extending main frame, a pair ofskis, each respectively mounted on the frame by a telescopic suspension,comprising a first upright tube fixed to the frame and a second tubereciprocably and swivelly mounted in the first tube and having a lowerend connected to one of the skis, and a rear suspension suspending adrive track beneath a rear portion of the frame for resisting upwardmovement of the track relative to the frame comprising at least onemember having one end pivotally mounted on the frame and a torsionspring connected between the frame and the member and including anadjustably fixed free end movable in opposite first and seconddirections to respectively increase and decrease resistance to the onemember moving toward the frame, the improvement comprising: linkagemeans connected between the second tubes and the free end of the torsionspring for moving the latter in the second direction in response to thesecond tubes moving upwardly within the first tubes to thereby softenthe rear suspension in anticipation of engaging whatever caused upwardmovement of the second tubes.
 3. In a snowmobile having a frame, a pairof skis suspended from the front of the frame by a front suspensionincluding a pair of upright struts, each including an outer tube fixedto the frame an inner tube telescopically and rotatably mounted in theouter tube, a shock absorber and spring assembly mounted between theframe and each of the inner tubes and including a spring biasing theinner tubes toward a normally extended condition, a drive tracksuspended from a rearward portion of the frame by a track suspensionincluding a track engaging assembly, a link assembly connecting thetrack engaging assembly to the frame, and a torsion spring assemblyconnected between the track engaging assembly and the frame and actingto bias the track engaging assembly away from the frame, the improvementcomprising: said torsion spring assembly having adjustable end meansmounted for movement in a first direction from a preselected normalposition for effecting decreasing torsional load in the spring; and astabilizer linkage means mounted between the front suspension and theadjustable end means for effecting movement of the latter in said firstdirection in response to upward telescopic movement of the inner tubesof the struts to thereby soften the rear suspension in anticipation of abump which is being encountered by the skis.
 4. The snowmobile definedin claim 1 wherein the motion transfer means includes a stabilizer barrotatably supported on the frame in horizontal, transverse relationshipadjacent the pair of skis and further includes a pair of first linkagesections respectively connected between the opposite ends of thestabilizer bar and the pair of front members and a second linkagesection connected between the stabilizer bar and element of the secondbiasing mechanism.
 5. The snowmobile defined in claim 2 wherein thelinkage means includes a sleeve reciprocably mounted on each first tubeand a lost motion connection means connecting the sleeve to an adjacentsecond tube for reciprocable but not swivel movement with the latter. 6.The snowmobile defined in claim 5 wherein each sleeve has at least onepin fixed thereto; at least one slot extending lengthwise in each firsttube; at least one slot in each second tube extending crosswise to andoverlapping the one slot in an adjacent first tube; and the pin beingreceived in both the one slot in the first tube and the one slot in thesecond tube.